1. Field of the Invention
The present invention relates to both a method and apparatus for providing telephone answer supervision capable of detecting the completion of both national and international calls, which employ different answer confirmation formats, as well as to an autonomous pay telephone, such as a mobile telephone, incorporating the same.
2. Background Discussion
Conventional pay telephone service, which has generally been provided by major telephone companies, is becoming highly attractive to the private pay station owner as a result of the continuing deregulation of such service and associated equipment as well as due to the availability of various mobile radio communication methods and systems in addition to the traditional landline telephone systems now in service.
One important requirement for all telephone configurations, landline or mobile as well as pay or otherwise, is the ability to determine if a placed call has been answered, hereinafter referred to as answer supervision. This requirement is essential in order to determine when to charge the patron for a placed telephone call. In fact, due to the past failure to properly provide effective answer supervision, recent legislation passed by the U.S. Congress has codified the requirements for answer supervision in the United States.
Typically, the Central Office of the local telephone company detects when the called party lifts the hand-set creating an off-hook condition which completes an electric loop from the Central Office. The telephone company starts billing the call from the moment it detects the loop completion. This answer supervision information is passed on to inter-exchange carriers, i.e., AT&T, MCI, under what is called in the United States as Feature Group D interconnection. Other methods used for detecting when a call has been answered include: 1) voice detection, 2) ring cadence interruption detection plus busy cadence acknowledge, and 3) timing after last digit dialed.
Normally, the conventional landline pay telephone is provided with no answer supervision capability and is dependent on the Central Office equipment (compatible with the national format only) to detect a completed call. In this regard, once the Central Office detects a completed call, it generates standard tones or signals (momentary reversal of polarity or signal tones, such as at 12,000 Hz) which are detected by the pay telephone to indicate the completion of a call. In the case of telephone companies following the North America standards, the pay telephone is connected to special lines at the Central Office which have the necessary equipment to provide the answer supervision signalling to the pay telephone. In the case of telephone companies following the international CCITT/CEPT standards, the Central Office either follows a similar reverse polarity method of answer supervision signalling or sends the tones to signal that the called party has answered, together with the appropriate rate information. Further, special circuits are generally provided at the Central Office that briefly reverse polarity of the line so that the pay telephone can collect deposited money once the Central Office detects the completed call.
In the case of customer owned pay phones (COCOT) or in the case of PBX, key systems, or even in the early days of MCI and US Sprint, the Central Office does not send any signal to the calling party indicating when the call has been answered. Therefore, the above-noted methods of answer supervision have been used with various algorithms to try and improve their inherent shortcomings. False answer detection or no detection when a call is really answered, resulting in erroneous charges or no charges at all, are the consequences of inexact answer supervision.
U.S. Pat. No. 4,916,733 discloses a telephone call answer supervision apparatus which employs the ringing cadence interruption detection method wherein the answer supervision signal received from the Central Office is employed to detect when the call is answered using the U.S. standard tone specs only. This arrangement measures the timing cadence of tones received and uses them as a reference for detecting a call. However, if a call is made to a country with a different timing cadence, this arrangement cannot recognize and differentiate the tones one from another because no provision is made to identify them.
U.S. Pat. Nos. 4,777,647, 4,924,497, 4,926,468 and 4,926,469 disclose pay telephone interface circuits for coupling a conventional pay station telephone to a telephone switching system. In this particular arrangement, the interface provides supervision signal detection functions normally provided by the switching system and thus can be connected thereto by a less costly business line.
U.S. Pat. No. 4,920,562 discloses an arrangement which can locally generate records of individual telephone calls to facilitate the billing of collect calls and calls placed using credit cards and other billing access formats on a pay telephone station. The station records the duration of the call and other pertinent information in a billing record for later retrieval to prepare the billing of the call. However, no provision is made for displaying the cost of the call in real time. Additionally, U.S. Pat. No. 4,890,317 similarly relates to an arrangement for locally generating records of individual telephone calls and includes an arrangement for determining the validity of the billing account number by attempting to place a telephone call using the billing account number to a controlled telephone number.
U.S. Pat. Nos. 4,658,096, 4,737,975, 4,775,997 and 4,922,517 all disclose cellular phone interface arrangements for providing a connection to adapt a standard telephone set with a radio transceiver. However, such an arrangement would suffer from the disadvantages noted above in that dependence on the traditional telephone landline systems is required when placing a call using such an arrangement.
Also known is a cellular mobile telephone credit card system such as disclosed, for example, by U.S. Pat. No. 4,776,003, in which the cellular pay station, from the viewpoint of the serving cellular carrier facility, is indistinguishable from standard cellular mobile stations. In this arrangement, the activities of the credit card station are supported by an administrative processor which is connected to a standard telephone line of the public switching telephone network. Data messages are exchanged therebetween and used to establish operating options, compilation of records for assignment of billing responsibility to transient customers and control of the stations for administrative and commercial reasons. As with the previously discussed pay telephone arrangements, the unit operates in dependence on the Central Office signaling scheme.
Because of the unique nature of a pay telephone using a mobile telephone installed, for example in a vehicle, special provisions are required for autonomous operation control in the areas of tariffing, call generation and accounting, called party detection, i.e., answer supervision, as well as accessing the cost of the service to a user. In view of the foregoing, it is highly desirable to provide mobile pay telephone equipment capable of accepting, on site, different tariffing formats as well as having the capability of detecting any type of national and international answer supervision confirmation. Because mobile pay telephone equipment operates in the radio environment, and therefore is highly mobile, it is also desirable that such an arrangement operate independently from the Central Office signaling scheme by providing a reliable interface with the particular radio receiver and autonomously generate the necessary supervisory signals required to operate with the telephone network.